1. Field of the Invention:
The present invention relates to a light-weight type linear ball bearing, and more particularly, to a light-weight type linear ball bearing suitable for use in small-size machines with a relatively small load, such as the sliding sections of various types of optical measuring instruments or small-size electronic computers.
2. Description of the Prior Art:
A known light-weight type endless linear motion ball bearing made of a thin steel plate which is pressed into a predetermined shape by utilizing plastic deformation is disclosed, for example, in the specification of Japanese Patent Laid-Open No. 136018/1986.
FIGS. 10 and 12 are respectively perspective and cross-sectional views of a known light-weight linear ball bearing. In the figure, a bed 1 serving as an outer casing is made of a thin steel plate pressed into a shape having flange portions along its two lateral edges. A table 2 serving as an inner casing is also made of a thin steel plate pressed into a similar shape having flange portions along its two lateral edges. The opposing surfaces of the two flange portions of the bed 1 and the table 2 are provided with track grooves 1a and 2a, respectively. Between the bed 1 and the table 2, an upper lid 5 and a retainer 6 are fixed to a lower lid 5 in which ball rolling direction changing passages and return passages 5b are formed as one unit in such a manner that a large number of balls 3 can be rolled therethrough.
In a ball bearing arranged in the manner described above, since the upper lid 5 is incorporated between the table 2 and the lower lid 5 so as to form one wall of the ball rolling passages and prevent escape of the balls, the table 2 is located at a higher position when the ball bearing is assembled, i.e., the distance H between the upper surface of the table 2 and the center of the loaded balls 3 is increased by a value which corresponds to the thickness of the upper lid 4, as shown in FIG. 11, thereby increasing the moment caused by the lateral loads applied to the table 2 and adversely influencing the rigidity of the table 2.
The retainer 6 is also disposed within the bed 1 in such a manner as to prevent the loaded balls 3 from escaping from the ball rolling grooves 1a and 2a. The retainer 6 has a shape such as that shown in FIG. 12. The provision of the retainer 6 increases the number of parts, the working processes of pressing and assembly, and the production cost.
FIG. 13 shows the structure of another type of known linear ball bearing which lacks the retainer 6. In this ball bearing, the upper lid 4 and the lower lid 5 have extended portions 4a and 5a, respectively, and the distal ends of the extended portions 4a and 5a located on each side of the upper lid 4 and the lower lid 6 are provided with inner protrusions 4b and 5b, respectively, which allows them retain the loaded balls 3 without the retainer.
However, this structure also fails to eliminate the need for the upper lid 4, and therefore cannot solve the problem involving the rigidity of the table 2 in relation to the lateral loads.